A fourth generation (4G) mobile communications method, which is the next generation mobile communications method of International Mobile Telecommunication 2000 (IMT-2000), has been under development.
The 4G mobile communications method is expected to flexibly support a multi-cell environment including a cellular system, and an isolated cell environment such as a hot spot area and an indoor environment, and increase frequency utilization efficiencies in both cell environments.
Regarding a link from a mobile station to a base station (referred to as an uplink, below) in the 4G mobile communications method, the following radio access methods have been proposed. As a single carrier transmission method, a Direct Sequence Code Division Multiple Access (DS-CDMA) method, an Interleaved Frequency Division Multiple Access (IFDMA) method, and a Variable Spreading and Chip Repetition Factors-CDMA (VSCRF-CDMA) method are proposed, for example (see Japanese Patent Application Laid-Open Publication No. 2004-297756, for example).
As a multi-carrier transmission method, an Orthogonal Frequency Division Multiplexing (OFDM) method, a Spread OFDM method, a Multi-Carrier Code Division Multiple Access (MC-CDMA) method, and a Variable Spreading Factor Spread OFDM (VSF-Spread OFDM) method are proposed, for example.
The single carrier methods can reduce power back-off of a transmission power amplifier, which leads to better energy efficiency because peak power is low, as far as power consumption in a mobile station is concerned.
In addition, from a viewpoint of transmission power limitations in a user terminal device, the single carrier transmission methods, which may have a low peak-to-average power ratio (PAPR) and high transmission amplifier efficiency, are suitable. In addition, coverage can be increased by applying the single carrier transmission because a transmission signal can reach farther away.
On the other hand, the user terminal device is required to transmit a wideband propagation path state measuring signal in order to transmit data using a band that can provide a better reception state in a frequency scheduling method that utilizes propagation path variations caused by frequency selective fading in the frequency domain.